Aluminum oxide is a general purpose abrasive material—it is a less expensive material that ceramic or zirconia alumina. Alunimum oxide is often called alumina in various other applications and is used in a wide array of abrasive products due to its characteristic high hardness. It's also used widely in these applications because the more expensive materials, ceramic and zirconia alumina, are often not needed in finer grits than 120 grit due to offering little over alumina oxide due to lower heat and durability requirements. Fundamentally, as the grit start to move higher (finer) than 120 grit, there is no benefit more expensive materials. This makes aluminum oxide a fantastic material for the majority of grits on soft to medium hardness materials that need to be shaped or grinded down.